3 It would be nice to think that you could just go and buy any computer,
4 install a bit of software on it and start using it to record and create
5 music. This idea isn't wrong, but there some important details that it
9 Any computer that you can buy today (since somewhere around the end of
10 2012) is capable of recording and processing a lot of audio data. It
11 will come with a builtin audio interface that can accept inputs from
12 microphones or electrical instruments. It will have a disk with a huge
13 amount of space for storing audio files.
16 When you are recording, editing and mixing music, you generally want to
17 work with very little <dfn>latency</dfn> between the time that
18 a sound is generated and when you can hear it. When the audio signal
19 flows through a computer, that means that the computer has to be able to
20 receive the signal, process it and send it back out again as fast as
22 And that is where it becomes very important <em>what</em> computer system
23 you have, because it is <strong>absolutely not</strong> the case that any
24 computer can do this job well.
27 Routing audio through a computer will always cause some delay, but if it
28 is small, you will generally never notice it. There are also ways to work
29 in which the delay does not matter at all (for example, not sending the
30 output from the computer to speakers).
33 The latency that you want for working with digital audio is typically in
34 the 1–5 ms range. For comparison, if you are sitting 1 m
35 (3 ft) from your speakers, the time the sound takes to reach your
36 ears is about 3 ms. Any modern computer can limit the delay to
37 100 ms. Most can keep it under 50 ms. Many will be able to get
38 down to 10 ms without too much effort. If you try to reduce the delay
39 on a computer that cannot meet your goal, you will get clicks and
40 glitches in the audio, which is clearly extremely undesirable.
43 <h2>Hardware-related Considerations</h2>
44 <dl class="wide-table">
45 <dt>Video interface</dt>
46 <dd>Poorly engineered video interfaces (and/or their device drivers) can
47 "steal" computer resources for a long time, preventing the audio interface
48 from keeping up with the flow of data</dd>
49 <dt>Wireless interface</dt>
50 <dd>Poorly engineered wireless networking interfaces (and/or their device
51 drivers) can also block the audio interface from keeping up with the flow
53 <dt><abbr title="Universal Serial Bus">USB</abbr> ports</dt>
54 <dd>If you are using an audio interface connected via USB, and sometimes
55 even if you are not, the precise configuration of your system's USB ports
56 can make a big difference. There are many cases where plugging the
57 interface into one port will work, but using different USB port results
58 in much worse performance. This has been seen even on Apple systems.
60 <dt>Internal USB Hubs</dt>
61 <dd>Ideally, you'd like your USB ports to all connect directly to the
62 main bus inside the computer. Some laptops (and possibly some
63 desktop systems) come wired with an internal USB hub between the
64 ports and the system bus, which can then cause problems for various
65 kinds of external USB devices, including some models of audio
66 interfaces. It is very difficult to discover whether this is true or
67 not, without simplying trying it out.</dd>
68 <dt><abbr title="Central Processing Unit">CPU</abbr> speed control</dt>
69 <dd>Handling audio with low latency requires that your processor keeps
70 running at its highest speed at all times. Many portable systems try to
71 regulate processor speed in order to save power—for low latency
72 audio, you want this totally disabled, either in the BIOS or at the OS
74 <dt>Excessive Interrupt Sharing</dt>
75 <dd>If your audio interface is forced by your computer to share an
76 interrupt line (basically a way to tell the CPU that something needs
77 its attention) with too many, or the wrong, other devices, this can also
78 prevent the audio interface from keeping up with the flow of data. In
79 laptops it is generally impossible to do anything about this. In many
80 desktop systems, it is possible at the BIOS level to reassign interrupts
81 to work around the problem.</dd>
82 <dt><abbr title="System Management Interrupt">SMI</abbr>s</dt>
83 <dd>SMIs are interrupts sent by the motherboard to tell the computer
84 about the state of various hardware. They cannot safely be disabled,
85 but they can also take a relatively long time to process. It is better
86 to have a motherboard which never sends SMIs at all—this is
87 also a requirement for realtime stock trading systems, which have
88 similar issues with latency.</dd>
89 <dt>Hyperthreading</dt>
90 <dd>This technology is becoming less common as actual multi-core CPUs
91 become the norm, but it still exists and is generally not good for
92 realtime performance. Sometimes you can disable this in the BIOS,
93 sometimes you cannot. A processor that uses hyperthreading will be
94 less stable in very low latency situations than one without.</dd>
95 <dt>Excessive vibration</dt>
96 <dd>This doesn't affect the flow of data to/from the audio interface,
97 but it can cause the flow of data to/from your disk storage to become
98 <em>much</em> slower. If you are going to use a computer in an
99 environment with loud live sound (specifically, high bass volume),
100 make sure to place it so that the disk is not subject to noticeable
101 vibration. The vibrations will physically displace the head-write
102 heads of disk, and the resulting errors will force a retry of the
103 reading from the disk. Retrying over and over massively reduces the
104 rate at which data can be read from the disk. Avoid this.</dd>